Rapidly solidified Sm-Co-Hf-B magnetic Nano-composites: Experimental and DFT studies

The effect of Hf and B additions on the phase stability, microstructure and magnetic properties of the metastable SmCo₇ (1:7H) ribbons has been investigated with a combined approach of experimental measurements and first principle DFT (density functional theory) calculations. A series of (Sm_0.12Co_0.88)₉₅Hf_5−xB_x (x = 0, 1, 2, 3, 4 and 5) alloys were arc-melted in a TIG (tungsten inert gas) arc melting furnace, followed by melt-spinning onto a copper roller at a wheel velocity of 40 m/s. Characterization based on X-ray diffraction indicates that the major phase is SmCo₇ having meta-stable (TbCu₇-type) structure. From the total energy calculations using DFT, the phase stability of (Sm_0.12Co_0.88)₉₅Hf_5−xB_x ribbons have been confirmed. Moreover, Hf and B addition results in an effective grain refinement; average grain size being as low as ~ 80 nm. The reduction in grain size leads to significant changes (increase or decrease) in magnetic properties depending on the Hf/B ratio. The coercivity value (H_c) varies between 7 kOe and 12 kOe as x (at.% B) increases from 0 to 5 at.%. The experimental coercivity values have been compared with the computed anisotropy energies. The saturation magnetization (M_s) increases from ~ 54 emu/g to 77 emu/g with increasing B concentration (x).